Manufacture of electric incandescent lamps and similar devices



May 10, 1960 J. N. BOWTELL ETAL 2,935,825

MANUFACTURE OF ELECTRIC INCANDESCENT LAMPS AND SIMILAR DEVICES Filed Feb. 27. 1957 2 Sheets-Sheet 1 I vs N-I'O'RS (/qwes A ORMH F0 Jmw 'qLmKD MOE- ZZAL JRQL 1 l TTORNEYS y 0, 1960 J N BOVLYTELL ETAL 2,935,825

MANuFAcTiJREi OF E ECTRIC INCANDESCENT, LAMPS AND SIMILAR m-zvrczs Filed Feb. 27. 1957 I 2 Sheets-Sheet 2 Fig.4

INVEN TORS \lwwes Amv v BOWTE'LL \Auv l -mezb 4/0026 James Norman Bowtell, Wembley, and John Alfred Moore, Neasden, London, England, assignors to The General Electric Company Limited, London, England Application February 27, 1957, Serial No. 642,741

Claims priority, application Great Britain February 28, 1956 8 Claims. 01. 53-7 This invention relates to the manufacture of electric incandescent lamps and other devices which are like such lamps in that they have a sealed evaucated or gas-filled envelope, the interior ofwhich is required to be substantially free from impurities.

During the manufacture of electric incandescent lamps of the standard type having a bulbous gas-filled envelope employing a single pumping stem the interior of the envelopes are flushed out several times with a suitable gas, for example clean nitrogen, to remove impurities, before introducing the final gas filling and sealing off, this flushing being effected by repeatedly filling the heated envelope with the gas and then evacuating it, so as progressively to dilute the impurities released by the heating of the envelope from surfaces within the envelope, and especially from the internal surface of the envelope itself. The purity of the final gas filling depends, amongst other things, upon the cleanliness of the flushing gas and on the number of flushings carried out, and in some cases the envelopes require to be flushed as many as ten or more times before the introduction of the final gas filling.

" l a tented May 10, 1 960 p re duced into the envelope through a tube whose external diameter is smaller than the internal diameter of the pumping stem and which has been inserted into the pumping stern until the orifice of the tube lies within the envelope, and the flushing gas is withdrawn, together with the impurities flushed out by it, through the space between the stem and the said tube.

, By employing such a method of flushing, a unidirectional flow of the flushing gas is obtained and the possibility of impurities being re-introduced into an envelope after having left it is avoided; similarly, the risk of im purities being introduced into the envelope from the support which carries the envelope during the flushing is reduced. The internal and external diameter of the flushing tube employed in a method in accordance with the invention for introducing the flushing gas will, of course,

Similarly, in the manufacture of vacuum lamps it is sometimes the practice to flush the lamp out several times lamp out several times with a suitable gas before finally evacuating and sealing the envelope.

However, one disadvantage which is present with the above method of flushing is that since theingoing and outgoing gases use a common path during their introduction into and withdrawal from the envelope respectively, there is a possibility of impurities which are withdrawn from the envelope being reintroduced therein as each new charge of flushing gas is led into the envelope. Thus in many cases a complex valve system is required for controlling the evacuation and flushing processes, and this often forms a trap for some of the impurities withdrawn from the envelope during its evacuation, the impurities trapped thereby tending to be carried into the envelope with a subsequent introduction of the flushing gas. over, other impurities may be present within the mounting which carries the envelopes during the flushing process and these may be introduced into the envelopes in some cases.

More

The main object of the present invention is to provide A a similar kind, required to be relatively free from irnw purities, and in which it is desired to flush out the en-, velope before sealing off.

According to the invention a method of flushing the interior of the envelope of an electric incandescent lamp or like device whose envelope has only a single pumping stem, during or immediately following a heating of the envelope forthe liberation of gaseous impurities. from Surfaces within the envelope, the flushing gas in introdepend on the dimensions of the device being flushed, in particular on the bore of the pumping stem, and also on the pressures used in carrying out the flushing process. In the case where the envelope is required to contain a filling gas, the flushing process should, of course, be carried out just before the introduction of the gas filling, although in some cases, for example where the filling gas is not the same as that used for flushing, the envelope may require to be evacuated between the flushing and filling stages.

The invention can be employed in arrangements in which the envelope is repeatedly filled with flushing gas and exhausted, and has the advantage that the vacuum pump may be connected to the pumping stem COIIlIIIlU', ously, so as to have a continuous envelope-exhausting action throughout the flushing process, the flushing gas being introduced into the envelope in a succession of pulses.

Alternatively there can be maintained between'the points of entry of the flushing gas into the envelope and its exit from the pumping stem, a continuous pressure difference during the whole of the flushing process such that a continuous unidirectional flow of the finishing gas is obtained. Preferably a vacuum pump is then used for reducing the pressure at the point of exit of the flushing gas from the pumping stem to a value considerably less than. atmospheric pressure for enabling a rapid flow of the flushing gas to be obtained whilst enabling the pressure within the envelope't'o be maintained at less than atmospheric pressure, thereby facilitating the release of impurities from the internal surfaces of the envelope. By the use of a suitably high pressure difference the time necessary to effect the cleansing of the envelope can .be reduced to a small fraction of that required when employing known flushing techniques involving repeated steps of evacuating the envelope and subsequently filling it with the flushing gas.

Thus a single flushing of the envelope of an electric incandescent lamp employing-thelatter method takes, on an average, about three to five seconds to effect with' present day'lamp-making machinery, depending on the volume of the envelope, the dimensions of the pumping stems and the efficiency of the vacuum pump, the complete flushing taking several times longer, depending on the number of individual flushings required. In the method in accordance with the present invention, by arranging that the pressureat the point of exit of the flushing gas from the pumping stem is of the order of 0.5- millimetre mercury, and the pressure at the point of: entry into the envelope such that a pressure of about 20 millimetres of mercury is maintained within the envelope,

a complete change of gas can be effected in about 0.5 second with an envelope of internal volume about 200; ccffand of the bulbous shape usual forincandescent; lamps. Its; has been found that satisfactory flushing 9f such a lamp envelope can'be eifected in about 15 sec! onds, which is less-than half the time required in most known methods. 7

In addition several operations of a complex valve system during the flushing of a single envelope are not required as they are in the known arrangement where the envelope is repeatedly'evacuated and filled with flushing gas. 'Morover, in arrangements for flushing envelopes intended to be filledwithone or more gases at apressure ofseveral hundred millimetres mercury, a vacuum pump able to reduce the pressure within the'envelope to only a few hundredths of a millimetre of mercury, as usual with the known arrangements, is not required since the impurities are swept out'by the flow of flushing-gas rather than progressively diluted as in known methodsof flushing.

The final gas filling, where oneis-required, is preferably also introduced into .the envelope through the Hushing tube before the withdrawal of the tube from the pumping stem.

1n the case of electric incandescent lamps of the gasfilled type, the flushing gas is preferably nitrogen, or a mixture of nitrogen and argon as used for thefinal gas filling. The flushing gas may be released to the atmosvV shape, the aperture of the stem within the envelope lying'between-the'two arms of theV. If the invention is to be applied with devices in which the aperture of the pumping stem within the envelope lies 7 to the side of the axis .of the main part of the stem, the

phere as in most known flushing processes, although in 7 some cases, especially where a mixture of argon and nitrogen is used for the flushing gas, means may be employed, if desired, for trapping the gas mixture after it has left a lamp envelope, so as .to enable it to be re-used for flushing purposes after being cleaned.

In most known methods of manufacturing the gas-filled type of lamp, it is usual to seal the lamps after they have cooled and their internal pressure is below atmospheric, in order to facilitate the sealing process, the cooling of the lamp envelopes being accelerated by blowing cool air onto them during the flushing process. Since the flushing process in accordane with the present invention can be effected much more rapidly than by most known methods, there will not usually be time for the envelope to have cooled sufficiently for this to be done immediately afterfthe completion of the flushing process, and inorder to save further time in the manufacture of the lamps, it may be desirable to seal the envelopes whilst they ,are

still hot, and whilst the internal filling pressure is above atmospheric, .so that the filling pressure fallsto .the re quired final value on the cooling of the lamp after sealing off. Any suitable known method ofsealing envelopes having internal pressures in excess of atmosphericvmay be employed for the sealing process.

Apparatus for carrying out the flushing of envelopes of incandescent lamps or like devices having a single pumping stem (hereinafter referred to simply as'lamps) before sealing may comprise an exhaust chamber connected or arranged to be connected to a vacuum pump, means for connecting the exhaust chamber to'the pumping stem of a lamp for exhausting the lamp envelope in use of the apparatus, and a tube extending hermetically but slidably through an aperture in part of the .wall of said chamber with its axis aligned with the axis of the pump ing stern of a said lamp when mounted in the apparatus, said tube being arranged to be connected outside the exhaust chamber to a source. of gas for flushing the interior of the lamp envelope and being connected within the chamber to a flushing tube which is movable with it relatively to the chamber, the arrangement being such that in operation of the apparatus the flushing tube can beinserted into the pumping stem of a said lamp until its :orifice lies withinthe lamp bulb, for the introduction ofthefiushinggas into theenvelope, and withdrawn'from the pumping stem after the envelope has been flushed,

for enabling the pumpingstem to be sealed off.

. For-enabling the flushing tube to be inserted readily into the envelope, the devices with which the method and apparatus of the invention are used are preferably constructed so that the aperture of the pumping stem within the envelope lies --substantially on the axis of the main flushing tube should be sutiiciently resilient to ensure that on the introduction of thetube into the stem the free end of the tube tfollows th e curvature of the stem until it emerges from the aperture 'at the end of the stern within the envelope. With such devices special care might need to be taken in forming the said aperture, possibly involving the use of a shaping tool, for ensuring that the flushing tube can be inserted through the pumping stem into the envelope, and the pumping stem should itself be arranged to have a smoothly curved internal surface at .the end within the envelope so as to enable the flushing tube readily to follow the contour of the stem.

One method of, and apparatus for, flushing the bulbof an electric incandescent lamp of the gas-filled type in accordance with the invention, will now be described by way of example with reference to Figures 1, 2, 3 and 4 of the accompanying schematic drawing, in whichFigure '1 shows a sectional view of part of the apparatus employed in carrying out said method, before the introduction of the flushing gas, Figure 2 shows a sectional view of part of the apparatus, at right angles to that shown in Figure ,l, as the flushing process is being carried out, Figure '3 shows a plan section of a lamp during the flushing process across the line XX in Figure 2, and Figure 4 shows the apparatus employed in flushing a different form of lamp from that illustrated in Figures 1 to 3.

Thus referring to Figure'l of the drawing the apparatus comprises a flushing head 1 in which a lamp bulb '2, having the pinched foot-tube 3 sealed thereto but with the pumping stem 4 not yet sealed off, is arranged to be mounted for carrying out thefiushing process, the bulb 2 being supported in the manner shown with the stem 4 extending'downwa'rds through an apertured rubber gland 5 arranged to grip the stem as in known flushing and sealing apparatus.

The flushing head 1 comprises a tubular exhaust chamber 6 arranged with its axis vertical and provided near the top with an inwardly directed annular flange 7, on which the gland 5, in the form of a cylinder having ,a circular hole extending coaxially through it, rests with said hole in alignment with the hole 9 at the centre of the flange 7. V

The diameter and axial length of the gland 5 are such that it just fits within the member 6 and, whenresting on the flange 7, extends almost to the top of the member as shown.

The outer surface of the exhaust chamber 6 is threaded for a short distance from the upper end, and on to this threaded part is screwed an internally threaded cylindrical cap 10, closed at the top apart from a central hole 11 through which the stem 4 of the lamp bulb 2 projects. A thrust bearing 12 sandwiched between two annular metal washers 13 and 14 is interposed between the top of the gland 5 and the closed endof the cap 10, and as the cap is screwed further'on to the top of exhaust chamber 6 the gland is compressed between the lower washer ,14 and the flange 7, which causes it to grip tightly the stem 4 of the lamp and form a hermetic seal between the stem and the gland, the unscrewing of the cap allowing the gland 'to release the stem. A lever 15 is attached-to the cap 10 for facilitating the gripping and release of lamps carried by the-flushing head, and the screw threads are so assesses s arranged that the'stems of the lamps can be gripped and released with'only a partial turn of the cap 10. To the side of the exhaust chamber 6 .is welded a metal side tube 8 communicating with the interior of the chamber through an aperture in the wall, and connecting it to a vacuum pump 40 (see Figure 4) through a suitable control valve 41.

At its lower end the exhaust chamber 6 carries an outwardly extending flange 16 and to this is screwed a similar flange 17 projecting outwardly from a hollow cylindrical stub 18 of the same diameter as the chamber 6 and arranged coaxially with respect to it. A rubber gasket 19 between the stub and the bottom end of the chamber provides a hermetic seal between the two parts of the apparatus. The outer surface of the stub .18 is threaded in a similar manner to the top of the chamber 6 and similarly carries an internally threaded cylindrical cap 20, this cap being closed at its lower end. In addition the stub is provided at the top with an inwardly directed annular flange 21 between which flange and the closed end of the cap 20 is arranged a cylindrical apertured rubber gland 22, similar to the gland 5, a thrust bearing assembly 23 sandwiched between two annular washers 24 and '25 being similarly interposed between the closed end ofthe capi20 and the adjacent end of the gland 22. Through the hole at the centre of the gland 22 and a corresponding hole in the closed end of the cap 20 extends a hollow tube 26, and the cap 24 is adjusted so that the rubber gland 22 is compressed against the sides of the tube 26 by an amount which allows the tube to slide axially within the gland but at the same time forms a hermetic seal between the 0.1 millimetre and an external diameter of 1.2 millimetre,

the tube 28 communicating with the interior of the tube 26 through a small hole 29 in the centre of the disc 27. The disc 27 preferably extends into sliding contact with the inner surface of the exhaust chamber 6 for guiding the movement of the tube 26, and is perforated exteriorly of the tube 26 to allow gas to pass through the disc freely along the outer sides of the tubes 26 and 28. The lower end of the tube 26 is closed but the tube is connected through a side tube 30 and a flexible pipe 42 (see Figure 4) to a source 43 of flushing -gas, a further control valve 44 being included between the source, and the tube 26 for controlling the flow of flushing gas to the tube 26 in operation of the apparatus. The valve, 44 may, for example, consist, as shown schematically in Figure 4, of a valve member 46 biased towards a seating 41" by means of a spring 48, and movable away from the seating to open the valveby meanso'f a cam:49 or other suitable means. Other forms of control valve can, however, obviously beused if desired. A furthersource of filling-gas might in some-cases also be connected to the tube 26 through another control'valve (not shown),.as will be further explained later.

The tube 26 is arranged to slide axially between'two limiting positions in use of the apparatus and when the tube 26 is at its lowest position the top of the flushing tube 28 is arranged to lie just within the hole'9 at the centre of the annular flange 7 at the top of the exhaust chamher 6, the raising of the tube 26 to its upper limiting position causing the top of the flushing tube 28 to enter in to the stem 4 of a'lamp bulb 2 carried by the flushing head and to project into the interior of the bulb, preferably somewhat further thanthe position shown in Figure 2. In order to facilitate the entry of the top of the flushing tube into the bulb the pinch 31 of the foot tube 3 may, as shown more clearly, in Figures 2 and3, be formed with across-sectiomin planes perpendicular to the lamp axis, substantially in the form of the letter V with the glass support stem 32 for the filament supports 33 located at the apexlof the V, and the aperture ofthe umping stem 4 in alignment with the axis of the main part of the pumping stem and lying between the arms of the V. However in some lamps the aperture of the pumping stem within the lamp envelope may, as shown in Figure 4, lie to the side of the axis of the main part of the stem, and for flushing such lamps the flushing tube 28 should be suitably resilient so that it follows the curvature of the stem when inserted therein, as illustrated in the figure. In operation, after a lamp bulb 2, which is in a heated condition following the sealing of the pinch 3 thereto, has been placed into the supporting head and the stem 4 gripped by the compression of the gland 5, the air in the bulb is partly removed by connecting the exhaust chamber to the vacuum pump 40-whilst the tube 26 is at its lower limit of travel. After a period of about 1 to 2 seconds, the tube 26 is raised so that the top of the flushing tube enters the lamp bulb as described. Then, whilst the interior of the bulb is connected to the vacuum pump, which maintains the pressure in the exhaust chamber 6 at a suitably low value, for example, about 0.5 millimetre mercury, the flushing gas is allowed to enter the bulb through the flushing tube 28, the gas scouring the inside of the bulb and leaving by the annular gap formed between the flushing tube 28 and the stem 4 of the bulb 2, as indicated by the arrows in Figure 2. The turbulence of the flushing gas ensures good flushing, and sincethere is a continuous flow in one direction there is no danger of impurities, after leaving the bulb, being reintroduced-by the incoming gas.

The rate of introduction of the flushing gas'is preferably such that the internal pressure of the bulb is about 20 millimetres mercury and we have found that with this pressure the bulb is flushed, that is to say there is a complete change of gas within the bulb, in about 0.5 second, a continuation of the flushing process for about 15 seconds being found to be sufficient to give a good cleansing of impurities from interior of the bulb. In some cases it may be necessary to heat the envelope for at least part of the flushing process in order to assist in the release of impurities from the envelope wall, as is done in some known methods of flushing;

trol valves for successively evacuating the bulb and then filling with flushing gas, which is unavoidable with known methods of flushing, are not required. i

A further advantage of the arrangement in accordance with the invention is that the degree of gas-tightness at the glands 5 and 22 implied by the use of the term hermetic can be less than with comparable known arrangements, since any 'inleaking gas would tend to be drawn away by the vacuum pump rather than pass into the lamp bulb.

The flushing gas may, if desired consist of the gas mixture employed as the filling of the bulb after sealing off, for example a mixture of argon and nitrogen. Usually the flushing gas will be released to the atmosphere, although in some cases, especially where a mixture of argon and nitrogen isemployed, it may be desirable for the gas leaving the bulbs during the flushing process to betrapped and used again after purifying. Instead of the valve 44 being open continuously throughout the flushing 'process so as-to produce a steady flow of the flushing gas o the bulb .2, thm n gas fi n e be ntrod into ,the bulb through the flushingtube cash r] vis then lowered, and the stem 4 is finally sealed off. In other cases, however, a different gas from that required for the lamp filling, for example pure nitrogen, might be employed as the flushing gas, in which case separate sources offiushing gas and filling gas are required .to be .connectable to the tube 26 and the bulb should be evacuated completely between the flushing and filling processes. Where the gas used for flushing is the same as that of the final filling, such complete evacuation will, .ingeneral, not be necessary.

Owing to the reduction in the time needed for efiecting the flushing of the lamp bulb ascompared with exist- ;ingdlushing technigues,.the bulb does not have the same length of time to cool down, and it may therefore be desirable, in order to save further time in the manufacture of the lamp, to seal the bulb whilst its internal pressure is above atmospheric, and allow the pressure to fall to the required final value after cooling, for example to about 700 millimetres mercury. Any suitable known ,methods of sealing envelopes havinginternal pressures in excess of atmospheric can be employed for this purpose. .Sealing a bulb whilst hot has the additional advantage that the reabsorption of impurities by the internal sur- "face of the bulb, which sometimes occurs on cooling, is prevented. I a

It ,will be appreciated that in practice the machine employed for carrying out the flushing process will carry .a plurality of flushing heads, for example each congstructedas described by -way of example, ,in order to enablerit to be usedfor mass production processes. The machine may conveniently consist of a rotatable table carrying a plurality, say twenty, of flushing vheads arranged on the circumference of av circle centeredonthe axis of rotation, the unflushed lamps being ,each placed on the machine in an empty flushing head as the head reaches a predetermined position on rotation of the table, and the flushed and sealed lamps being removed from the flushing heads when they reach another-position; for example they may be transferred to further apparatus for the attachment of the lamp caps.

In a machine including a plurality of flushing heads as .aforesaidcarricd by a rotatable table the gripping and-release of the lamp stems by'the flushing heads, the raising and lowering of the tube 26, the introduction of the flushing gas and final gas filling and the operation of the valve in the vacuum yStem may all be arranged .to be effected automatically as the table rotates, for example by means of suitably arranged cams, and if desired automatically operated means may be employed .for transferring the lamps to and from the machine.

Weclaim:

1. A ,method of decontaminating the interior of ,a closed envelope of anelectric incandescent lamp or like electrical device in which the envelope .is of thekind purities flushedout by it, through the elongated annular spacebetween the stem and the said tubular member.

,2. A method according to claim 1 during which .a ,vacuum pump is connected to the pumping stem continuously, so as to have a continuous envelope-exhausting action, :and the flushing gas is introduced into the envelope through the said tubular member in a succession of pulses.v

3. A method according to claim 1 during which a continuous pressure difference is maintained between the points of entry of the flushing gas into the envelope and its exit from the pumping stem so that a continuous unidirectional flow of the flushing gas is obtained.

4. A method according to claim 3 wherein a vacuum pump is used for reducing the pressure at the point of exit of the flushing gas from the pumping stem to a value considerably less than atmospheric pressure so as to enable a rapid flow of the flushing gas to be obtained whilst the pressure within the envelope is maintained at less than atmospheric pressure.

5. A method according to claim 1 for flushing the envelope of a said electric incandescent lamp or like device which is required to have a gas filling after the sealing off, wherein the flushing of the envelope is carried out with a gas which is the same as the required gas filling.

6. A method of manufacturing a said electric incandescent lamp or like device having a sealed envelope containing a gas filling, wherein the envelope is flushed before sealing by a method according to claim 1 and wherein, after the completion of the flushing process, the final gas filling is introduced into the envelope through the saidtubular member before the tubular member is withdrawn-from the pumping stem.

7 Apparatus for carrying out the flushing of envelopes of incandescent lamps or like devices in which the envelopes are of the kind comprising a glass bulb having a single elongated pumping stem extending from the bulb comprising an exhaust chamber having an opening for receiving the pumping stem of a said envelope and means ,for hermetically closing the gap between the stem and theside of the opening when the stern has been inserted into theopening, means for connecting the exhaust chamher to a vacuum pump for exhausting the envelope in use of the apparatus, and a tube extending hermetically but slidably through an aperture in part of the wall of said chamber with its axis aligned with the axis of the pumping stem of the device when the latter is mounted in the apparatus, said tube being arranged tobe connected out- .side the exhaustcharnber to a source of gas for flushing the interior of the device envelope and being connected within the chamberto a flushing tube which is movable with it relatively to the chamber so that the flushing tube can be inserted into the pumping .stem of the device until its orifice lies ,within the bulb part of the envelope of thedevice forthe introduction of the flushing gas into theenvelope and withdrawn from the pumping stem after the envelope has been flushed for enabling the pumping stem to be sealed off.

Apparatus according to claim 7 designed for flushthe interior of theenvelopes of electric incandescent lamps, or like devices of the kind in which the, aperture of the'pumpingste n at the end within the envelope liesto the side of theaxis of the main part of .the stem so that the stem follows a curved path at that end, wherein the flushing tube isof such resilience that on being introducediinto thepumpingstem the free end of the tube can'follow the curvature of the stem until it emerges from said aperture. 

